1. Field of the Invention
The invention relates to the field of optical disk recorders and, more particularly, to means for detecting the presence of prerecorded data during writing of data on the optical disk.
2. Brief Description of the Prior Art
Most recording systems attempting to protect previously written data do so by building an index of the data written on the disk descriptive of the location and extent of the data. If the index failed, previously written data could be overwritten. However, the new data was usually correctly recorded and could be read.
In optical recording, it is not currently possible to write new data in disk areas having previously recorded data. A failure in the index leads to loss of both the old data and the new data. Reliance on an index only is not entirely satisfactory.
While it is possible to first read each and every data sector before writing data into the sector, unless an additional read head is employed, at least one extra disk revolution is lost reading a sector before writing in it can commence.